1. Field of the Invention
The invention relates to an apparatus for the manufacture of hot-rolled material comprising a continuous casting machine for casting a slab and reduction means in line with the continuous casting machine for reducing the thickness of the slab into a strip. The invention also relates to a method for the manufacture of hot-rolled steel.
2. Description of the Prior Art
An apparatus and method of the type mentioned above are known from the publication DE-OS-3840812. This known apparatus comprises a continuous casting machine for casting thin slabs and reduction means in the form of a four-high stand with four rolls. The continuous casting machine casts a slab with a thickness in the range 50 mm to 100 mm which the reduction means reduce to a thickness of approximately 25 mm. In order to achieve the desired reduction in thickness, it is usual to place several four-high stands directly one after the other. The entry temperature of the slab in the first four-high stand is of the order of 1100.degree. C.
A number of disadvantages are associated with the use of several four-high stands:
complicated arrangements are required for harmonizing the rolling speed between each of the several mill stands and with the casting speed of the continuous casting machine; PA1 there is high thermal loading of the work rolls of each four-high stand; PA1 temperature losses of the workpiece on the several mill stands are relatively high; PA1 there is high wear and tear on rolls as a result of the number of rolls (several work rolls); PA1 the long stay time in the rolling unit causes increased oxide layer formation; PA1 the end-to-end length of the rolling section is large; PA1 capital investment is high. PA1 simple control over rolling speed whereby the entry velocity of 8-0.1 m/min or slower lies PA1 adequately within the range of variation of the roll; PA1 low thermal loading of the work rolls due to their large dimensions; PA1 temperature losses of the workpiece are less; PA1 less wear and tear on the rolls; PA1 the period of exposure of the thin slab to the atmosphere is shorter so that less oxide forms; PA1 with a single mill stand, it is simpler to remove the oxide on account of the easier accessibility compared with several four-high stands; PA1 when removing oxide using high-pressure water jets, cooling takes place only once and not several times as is the case with several four-high stands.